The invention relates to an input document detecting system and method, more particularly, a system and method utilizing a code-modulated light beam to detect the presence or absence of an object in a high speed document scanner or the like.
A high-speed document scanner runs at 160 pages per minute (about 3 pages per second) using 8.5xe2x80x3xc3x9711xe2x80x3 size paper. It runs even faster using smaller sized documents, such as checks or business cards. It is difficult for an operator to feed a document manually into the scanner at such a high speed. In order to maintain throughput of the system, an Automatic Document Feeder (ADF) is used to supply a document to the scanner. With its adjustable guide, the Automatic Document Feeder is capable of handling documents, including paper, in a variety of sizes (from business card to B-size drawing), types (from onion-skin to cardboard), and colors. When the document/paper supply is empty, the Automatic Document Feeder tray will automatically be lowered, allowing the operator to load the next batch of documents. This general type of device has been included in an Automatic Document Feeder in the present invention to detect the emptiness of a document/paper supply tray. The device is mounted at the bottom of a document supply tray, where it monitors the back of the bottom sheet in the supply tray through an open hole.
In conventional printers, an optical sensor at the paper tray is used to detect the presence or absence of an uppermost sheet of paper at the start of the paper feed path. The optical sensor is often a photoreflector-type device mounted on a side of a guide on the paper tray. A light beam produced by the light source of the photoreflector device bounces off the sheet of paper, runs through a paper detecting circuit, and the presence or absence of the sheet is read. There will be no returned signal to the receiver of the optical sensor when the last sheet of paper, or other document, is fed.
To detect the presence of an object, a commonly used method measures the strength of returned energy. An AC or DC powered light source is used as a sending unit. The emitted light from the light source travels through the space, and collides with the surface of the object, such as a sheet of paper. Depending on the reflectivity of the object""s surface, some amount of energy is reflected and reaches the receiving unit. Based on the amount of the received energy, the state of xe2x80x9cpresencexe2x80x9d or xe2x80x9cabsencexe2x80x9d of the object is determined.
Although this conventional method is, in general, acceptable, it is heavily dependent on the reflectivity of the object surface, and the stability of the light intensity of the light source. Furthermore, the received energy may be polluted by ambient light.
Another problem with conventional object detecting methods and systems concerns the effective energy on the returned light due to the reflection from various color papers. Where the paper on the paper tray is different colors, such as red, green or blue, the presence of color seems to confuse the signals, resulting in errors. Gain levels can be readjusted on existing sensors, but a setting that is too high may saturate the sensor for some strong signal, resulting in errors. There are more types and colors of paper and other print media available now than ever before. However, object detection sensor technology for these new materials does not appear to have improved along with the material technology.
The present invention also sends out light beams from a light source and receives returned energy reflected from the surface of the targeted object light; however, the light beam is utilized as a carrier rather than a signal. The light beam is modulated with a coded signal. In the present invention, the received energy (signal) is magnified by a high gain AC amplifier, and then sent to the decoder to check for the presence of the code.
The method/system of the present invention is not sensitive to the stability of ambient light intensity, and is relatively unaffected by reflectivity of the object surface. There is no need to include ambient light sensors or have other compensations for reflectivity built into the system of the present invention. This invention is also immune to ambient light conditions. Thus, accuracy and reliability are increased, and operator frustration and wasted time are decreased.
The present invention is a method for detecting the presence or absence of an object, comprising the steps of:
(a) modulating a light source of a reflective-type optical sensor with a coded digital/analog signal;
(b) emitting a code-modulated light beam from the light source and directing it toward the object;
(c) collecting the reflected code-modulated light beam with a receiver portion of the optical sensor;
(d) forwarding the signal from the reflected light beam through an AC amplifier and amplifying it; and
(e) feeding the amplified signal to a decoder and decoding it.
Also included herein is an input document detecting system for detecting the presence or absence of an object, comprising:
(a) a modulator, and a driver;
(b) a reflective-type optical sensor having an analog output, the optical sensor comprising a light source for emitting a light beam; an IR transmitter; and a receiver portion for collecting a reflected code-modulated light beam, the receiver portion comprising a built-in IR filter;
(c) a high gain AC amplifier for amplifying the signal from the reflected light beam; and
(d) a decoder for decoding the signal from the amplifier;
wherein the modulator modulates the light beam from the reflective-type optical sensor with a coded digital/analog signal; and
wherein the light source emits a code-modulated light beam, which is directed toward the object.